Method of impregnating wood with wood-preserving oil



r 9,597 Un1ted States Patent *fifice METHOD OF IMPREGNATING WOOD WITH WOOD-PRESERVING OIL Richard E. Walker, Tulsa, Okla., and Grover L. Bridger and Lionel K. Arnold, Ames, Iowa, assiguors to Iowa State College Research Foundation, Inc, Ames, Iowa, a corporation of Iowa No Drawing. Application February 2, 1953, Serial No. 334,761

1 Claim. (Cl. 117-120) This invention relates to a method of impregnating a wood body with a wood-treating liquid.

The wood preservation industry has long used pressures above atmospheric to force liquid preservatives, fire retardant liquids, and other liquids into wood. Two general processes are used, the full cell or Bethall treatment, and the empty cell, either the Lowry or Rueping, treatment. In these treatments the wood to be impregnated is submerged in the liquid, the pressure on the liquid increased to force the liquid into the material, and then a vacuum is applied to the wood to remove the excess liquid. In the full cell or Bethall process the wood is subjected to a vacuum to remove the internal air, the wood submerged in the liquid while under a vacuum, and the liquid pressure increased to inject the liquid. This treatment gives very high liquid concentrations in the penetrated portion of the wood but excessive amounts of liquid are needed to cause deep liquid penetrations and the treatment is used only for a class of material such as piling, which require very large amounts of preservative and where little handling and personnel contact are necessary. In the Lowry empty cell process the wood is surrounded with the liquid to be impregnated at atmospheric pressure, whereas in the Rueping empty cell process the wood is first placed under air pressure to increase the internal air pressure within the wood, and then the wood is submerged in the liquid. Both empty cell treatments rely on injecting an excess of liquid and then removing the excess by applying a vacuum after the liquid impregnation. This is usually followed by a steaming period in an attempt to minimize bleeding, which is the flow of liquid to the surface of the wood after the treatment. While the Rueping process gives deeper penetrations than theLowry process, the penetration is erratic and the liquid bleedsthat is, comes from inside the wood to the surface after treatment. This not only causes loss of the liquid from the solid interior where it is desired but if the liquid is creosote or of an oil base preservative, such as the heavier oils used as a carrier for pentachlorophenol, the oily film and residue is objectionable to persons coming into contact with the surface and creates a fire hazard. While bleeding is less pronounced with the Lowry treatment it still occurs and can be eliminated only by reducing the amount of injected oil, thus obtaining only shallow penetrations and a poor treatment, or by using excessively long steaming periods which injure wood fiber and lower the strength, and therefore the quality of the product.

In the case of wood poles and other products in which part of the wood is in the ground and the remainder above ground, it is desirable to injecta heavy preservative concentration at the groundline whereas a lower concentration of preservative and a surface free of oil is needed above the groundline. In an attempt to accomplish this closely spaced longitudinal incisions about /2 inch deep are made at the groundline. Generally the empty cell treatments do not increase the penetration and preservative concentrations in the incised wood above that in the non-incised wood. Therefore in order to obtain deep penetrations a high liquid retention is necessary which adds to the cost of the treatment as well as resulting in bleeding in the aboveground portion of the Wood.

One object of this invention is to obtain deeper liquid penetrations with a smaller amount of liquid in the impregnation of wood bodies with a wood-treating liquid. Another object is to keep the liquid from coming to the surface. Another object is to obtain a more uniform distribution and to obtain higher liquid concentrations deep in the wood. Another object is to decrease the inflammability of the product. Another object is to produce a proportionally greater penetration and concentration in the incised than in the non-incised wood.

In one embodiment of this invention, the first liquid injected, liquid A, is creosote, or an oil base liquid preservative, such as a solution of pentachlorophenol in a petroleum hydrocarbon oil to increase the decay resistance of the wood, to dimensionally stabilize the wood, or increase its strength. Suitable petroleum oils for use as solvents have specific gravities from 0.825 to 0.934 at 60/60 F. The second liquid, liquid B, is relatively volatile compared to liquid A and is substantially immiscible in liquid A. Liquid B is preferably water, or an aqueous solution of a toxic chemical such as zinc chloride, or a fire retardent chemical, such as mono or diammonium phosphate, ammonium sulfate, boric acid, etc. The water also preferably contains a wetting agent, such as an alkyl aryl sulfonate or alkyl sulfate.

After the first liquid, liquid A, has been injected to the desired retention, liquid B is injected. The injection of liquid B increases the depth of penetration of liquid A as well as causing a more uniform distribution and, if liquid B is then removed, liquid A does not come to the surface. In other words, liquid B functions as a distributing liquid due to its immiscibility with liquid A. The injected liquid B can be removed Wholly or in part by vaporization either at atmospheric pressure or by application of a vacuum, provided that the wood contains suflicient heat or that heat is supplied during the vaporization. This is preferably accomplished by steaming. The vaporization of liquid B leaves within the porous structure any dissolved solids. Or if it is desired to remove only part of the injected liquid B a very uniform distribution of liquid B results.

This method of treatment produces a deeper penetration of liquid A for the same amount of injected liquid than the conventional empty cell methods of treatment. Further, liquid A is more uniformly distributed within the treated material by this method than by the empty cell methods of treatment and there is less tendency for the liquid A to come to the surface and leave an oily residue. Further, this method of treatment does not require long steaming periods and thus the wood is not injured. Further, this treatment not only produces a deeper penetration than the empty cell treatments in both the incised and non-incised wood but also a proportionally greater increase in penetration in the incised wood. Further, it gives a higher concentration of liquid A in the incised wood relative to the non-incised wood than the conventional empty cell treatments and a higher concentration deep in the wood.

The penetration of liquid A tends to increase as higher pressures are maintained during the change from. liquid A to liquid B and also as higher pressures of liquid B are used and as the duration of the impregnation of liquid B is extended. The change from liquid A to liquid B can be made at atmospheric pressure, but it is preferably made at super-atmospheric pressures. If it is desired to replace liquid A with liquid B at pressures above atmospheric pressure, then liquid A can be displaced directly with liquid B or liquid A can be displaced with compressed gas, such as air, and then the gas displaced with liquid B. However the penetration of liquid A Will be improved if the pressure during the change is suificient to substantially prevent liquid A from being expelled during the change from liquid A to liquid B. To illustrate this, if when treating refractory Douglas fir poles, it is desired to impregnate liquid A at 150 p. s. i. and the maximum usable compressed air pressure is 90 p. s. i., then after the desired quantity of liquid A is injected the pressure on liquid A could be reduced to and held at 120 p. s. i. for 30 minutes and then reduced to 90 p. s. i. and held for 30 minutes before replacing liquid A with compressed air, and the air in turn replaced with liquid B. The permeability of the wood would determine the rate of pressure reduction. Further the pressure on liquid B can be gradually reduced, during its impregnation, continuously or in stages to some lower pressure or to atmospheric pressure. Such a reduction in pressure will reduce the tendency to bleed.

Specific embodiments of the method of this invention are illustrated in the following examples.

Example I The following schedule of treatment of Douglas fir poles illustrates the preferred procedure. The poles are placed in a pressure cylinder and the cylinder is filled with oil solution of pentachlorophenol at atmospheric pressure and 150 degrees F. Then the pressure on the oil is increased to 150 p. s. i. and the impregnation continued until a retention of 6 pounds of oil per cubic foot of pole is obtained. The oil in the cylinder is then displaced with compressed air at 150 p. s. i. and in turn the compressed air is displaced With water at 150 p. s. i. and 200 degrees F. The Water is held in the cylinder for 6 hours, the first /2 hour at 150 p. s. i. and the remainder at 50 p. s. i. At the end of this time the water is removed from the cylinder and the wood subjected to steam at p. s. i. for 30 minutes. Immediately thereafter a vacuum of 22 inches of mercury is applied to the cylinder for 30 minutes and after this the poles are removed from the cylinder.

When treated with this type of schedule to retentions of 6 to 7 pounds of oil per cubic foot of pole, 99 percent of the sapwood in the incised groundline section and 91 percent of the sapwood in the non-incised section of the poles were penetrated. Treated to the same retention, the conventional Lowry method resulted in 89 percent of incised groundline sapwood penetrated and 82 percent of the non-incised midpoint sapwood penetrated. Further one third of the poles treated by this process to 6 to 7 pounds of oil per cubic foot of pole had heartwood penetration in the incised groundline and one fifth had heartwood penetration at the non-incised midpoint. None of the poles treated by the conventional Lowry treatment showed heartwood penetration.

Example II Douglas fir was treated in 150 F. oil at 150 p. s. i.

face and black color, whereas the wood treated with plain water remained dark in color and had a tacky surface for over a year.

Various alkyl aryl sulfonates and other wetting agents can be employed in the manner described in Example ll. It has been discovered that the incorporation of a wetting agent in liquid B, which is preferably water, has the surprising advantage that if some of the liquid A, which is preferably oil, does find its way to the surface the wood body, the wetting agent renders it relatively harmless by making it dry rapidly instead of remaining sticky. The reason for this effect is not understood. Moreover, the use of a wetting agent in liquid B does not have any collateral disadvantages as far as is known, although it might be expected to be undesirable. Specifically, it has been found that the use of a Wetting agent in water does not affect the penetration and distribution of the wood-preserving oil, nor does it increase the tendency of the oily liquid to flow from the wood interior to the surface of the wood body shortly after treatment. However, as indicated, if an oil film on the outside of the body does occur, it'will dry quickly.

The alkyl aryl sulfonates are the preferred wetting agents, but other types of wetting agents can be employed, such as the alkyl sulphates, the sulfonated fatty acid amides, and the sulfonated mono-glycerides. Specific examples of alkyl aryl sulfonates which can be employed are sodium or potassium dodecyl benzene sulfonate, sodium or potassium octadecyl benzene sulfonate, and sodium or potassium octyl napthalene sulfonate. Specific examples of the alkyl sulphates which can be employed are the sodium and potassium salts of dodecyl, hexadecyl and octadecyl sulphates.

Example III Large scale tests were conducted in the manner set out in Example 1 except that the oil pressure was decreased at the rate of 30 pounds per square inch in thirty minutes to 40 pounds per square inch, and then compressed air was introduced. Water pressure was then applied at pounds per square inch for thirty minutes and maintained at 150 lbs. per square inch for five and one-half hours.

While in the foregoing specification this invention has been described in considerable detail for the purpose of illustration and specific illustrative embodiments thereof have been set forth, it will be apparent to those skilled in the art that many of the specific details and embodiments describedcan be varied Widely without departing from the broad idea of the invention.

We claim:

in a process for impregnating a wood body with a wood-preserving oil, the method of improving the distribution of the Wood-preserving oil within the wood body characterized by the steps of forcing a wood-preserving oil into a wood body, and then forcing water containing a wetting agent into said wood body, said wetting agent being selected from the class consisting of alkyl aryl sulfonates, alkyl sulfates, sulfonated fatty acid amides, and sulfonated monoglycerides.

References Cited in the file of this patent UNITED STATES PATENTS 317,440 Card May 5, 1885 1,012,207 Kolossvary Dec. 19, 1911 1,198,040 Landau Sept. 12, 1916 1,585,860 Howald May 25, 1926 2,054,399 White Sept. 15, 1936 2,054,400 White Sept. 15, 1936 

